The quality of water, for example as provided by utility organizations to domestic households and the like ranges widely. In general, it has been observed to have diminished to the extent that a water quality enhancement industry has developed of significant proportions.
One generally less expensive approach to water quality improvement provides for the positioning of a filter at a faucet location where water is drawn for drinking and cooking purposes. Typically, this location is at the kitchen sink. The type filter desired for this application usually is of an "in-line" variety located within the water line ahead of or before the faucet at the sink. Such filters are quite simple, typically being provided as a retainer holding a filtration medium such as charcoal or the like used to remove contaminants. These filtration media have a limited capacity generally based on the number of gallons of water passing through them. Following a predetermined flow quantity, for example from 500 to 2400 gallons, the filtration medium must be changed, whereupon a next filtering period ensues. The number of gallons of water representing such filter capacity varies with the quality of water encountered, as well as with the filter used. Thus, a time estimate of useful filter life may be made based on these variables, as well as the extent of household use of water at the location of filtration. However, such estimates are inherently inaccurate and filter replacement is made in reliance on the householder's memory of the projected replacement date. Thus, a metering device is desirable for water use monitoring which remains inexpensive enough for the limited application at hand, but which is of a rugged and robust structure sufficient to withstand water line pressures, which typically are at 125 psi and can reach higher levels during water pressure excursions. For example, such devices should meet national criteria for performance at 400 psi.
In addition to measuring flow, these metering devices should be simply adjustable for accommodating various filter capacities and should provide some form of cuing to the user as to when time for replenishment is at hand. Installation of the meter and associated cuing logic should be simple in keeping with the noted cost criteria. In this regard, the utilization of electronics and associated power supply wiring or battery replenishment should be avoided. Generally, a turbine form of metering is contemplated for the purposes at hand, however, the rotational rate for such turbines, when used with purely mechanical metering structures requires a technique for rotation monitoring wherein the number of rotations may exceed 3,900,000. To achieve a necessary compactness while still carrying on such monitoring in a mechanical manner has posed difficulties to filter designers.